There are two core concerns here
One is easier to deal with than the other.
How do I get my own, and my groups hormones to be put away?
(We are a bunch of 8th and 9th graders).
You can't. You are normal people reacting normally to a social situation that you are in. What you can do is try to lessen its influence on the game's flow.
Can someone help me?
Yes. Before the next session starts, you need to have a discussion with your friends about the need to focus on the game during game play.
- A word about role playing games. Role playing games are by their
nature social situations that involve social behaviors. As a
DM, a large part of your role is facilitating everyone's fun as well
as your own.
- Your frustration with trying to keep a game moving while the social distractions are ongoing is shared by a lot of DMs for a lot of reasons regardless of age group. The social distractions can only be influenced, not controlled. Your positional authority as the DM, to get people to do things, is practically limited by how much your players accept that role's authority. Pushing too hard can cost you players and be un-fun for everyone. (You want to avoid that).
Set some basic expectations
What you can do and what you should do is have a discussion with everyone about Spotlight Sharing before your next game session. Regardless of your new player getting a lot of the Spotlight from her fellow players, make sure that you are understood: everyone gets a turn in the Spotlight. Taking turns is how that's done. Since part of your problem is the game being disrupted, three points to bring up are ...
Be ready to take your turn when it's your turn. This may sound obvious, but it is what keeps the game moving.
Get the whole group to agree on a time limit for each player's turn: 15, 30, 60 seconds, two minutes ... whatever. Then hold them to it. If need be, use a one minute egg timer, or the timer function on your (the DM's) cell phone or watch.
When someone else has a turn, pay attention to them. Each player's turn means, in the theatrical sense, that the Spotlight is on them. Get their verbal agreement that whoever's turn it is has the floor.
Listen, pay attention to who ever is taking their turn, be it in combat or out. If need be, write that on a card and hold it up now and again as a reminder. (Yes, I've done that before as a DM).
Special in-combat rule: If you don't take your turn in time, you 'dodge' and otherwise lose your turn.
DM-only points for your consideration:
Leave the item gifting alone. It will take care of itself in time, and it isn't a problem from the DM to solve. Interactions between the players like giving each other various imaginary items isn't where the DM needs to have a role when your players are your peers. Being heavy handed as a DM is a buzz kill, and often (at any age group) gets a strong push back from players.
If things get carried away in terms of losing the focus on the game, then as DM you ask clearly "So, what do you do now?" directly to one of the players (or the whole group) to get the attention directed back at the game.
What does that all have to do with your social problem?
That problem (boys and girls being attracted to each other) isn't "solvable" ... but if you get all of the players to agree to the basic premise of keeping the game flow going, then the social distraction's impact on the game will be reduced. You being attracted to her means one thing for you as the DM: be watchful, on yourself, for any blatant displays of favoritism.
Accept that the social interaction is a key part of why we play
Because it is. Focus on having fun, focus on rulings that promote having fun, and focus on keeping the game moving. Beyond that, there is only so much that you can control. Don't try to control what you can't.
And have fun.
Personal experience with distractions at the table
While playing in and DMing for mixed gender groups from late teens to adults, and in DM'ing for teenagers and pre-teens for a few years, I have found that what keeps a game group together (particularly at the age you are asking about) is the fact that you are having fun doing something together.
Distraction from play comes in a lot of forms; in your case it arises as flirting and too much attention paid to one player. The players are in control of what they do; what keeps distractions down -- in all age groups -- is to keep the pace of play moving. (Hence the advice above).
- This answer is based on the following assumption: you want to keep
playing this game with your friends -- all of them, to include your
new player.
My most relevant experience to your situation, with the flirting problem, was in an adult context (gamers were in their 20's). What I found most effective during play as the DM, when the flirting and relationship stuff cropped up as a distraction, was to say (the family friendly version of what I said)
"After we are done with the raid, you can go on your date; we can't all be on your date, so let's get back to that door that just opened ... "
Will something like that work in your group? You'll have to tailor it to your friends and how much they listen to you. If the flirting is getting out of hand, directly calling an orc an orc can be helpful.
Flirt on your own time, let's get this adventure going again ...
... is another way to get the point across. Since I don't know who the peer leader is in your group, in terms of whose personality is most powerful, how you phrase that will need to fit your group. A core part of your role as DM: getting the game to flow, to keep the play moving forward. Keeping the players' attention on the danger/adventure/situation is a way to keep the distractions down.
An option that depends on your circle of friends: invite another young lady whom you all know to join you at the table. That can change the social dynamics somewhat, but whether it solves this problem depends on the personalities.
After the questions edits, which non trivially changed the form of the question, I will leave this as an answer to the original question. The answers to address the groping (IC and OOC) concern in the linked question sufficiently address that problem which IMO warrants a separate and serious consideration. If the "can't keep their hands to themselves" issue comes up again, the bottom line from @RSid's answer is a good tool for stopping that in its tracks: a clear "Not Cool!" directed at whomever crosses that line.