On Combat on Aid Another says
In melee combat, you can help a friend attack or defend by distracting or interfering with an opponent. If you’re in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can attempt to aid your friend as a standard action. You make an attack roll against AC 10. If you succeed, your friend gains either a +2 bonus on his next attack roll against that opponent or a +2 bonus to AC against that opponent’s next attack (your choice), as long as that attack comes before the beginning of your next turn.…
Since the weapon will be in front line with you, I guess she is in a good place to Aid Another during combat. But, what about
If you’re in position to make a melee attack? If the DM considers that the aid should come from another attack that the one from the bearer or if he understands that the subject should be able to make an attack on his own, then the weapon wont be able to aid another in combat. (May depend of the type of sentient weapon).
On Skills on Aid Another says
You can help someone achieve success on a skill check by making the same kind of skill check in a cooperative effort. If you roll a 10 or higher on your check, the character you're helping gets a +2 bonus on his or her check. (You can't take 10 on a skill check to aid another.) In many cases, a character's help won't be beneficial, or only a limited number of characters can help at once.
For skill Aid Another, I guess she can help the best she can but she will be limited. Some skill can be hard to help without a body. See with your DM.
By the way, a black blade indeed prevents to pick a familiar but a black blade is not a familiar.
A black blade is bonded to a particular magus, much like a familiar, but in more of a partnership than a master-servant relationship.
A sentient weapon should be consider more like a partner. In fact, they should be treated as NPC.
Magic items sometimes have intelligence of their own. Magically imbued with sentience, these items think and feel the same way characters do and should be treated as NPCs
If the weapon can aid you? In any case, not if they are not willing to. Most of the time I guess the weapon will help you. You are a her bearer after all. Just be sure that if the sentient doesn't want to aid, as any NPC, she wont. Be respectful with your weapon.
Finally if you are wondering whether sentient item has actions, in fact they do.
Activating a power or concentrating on an active one is a standard action the item takes.
This answer is inpired from this one by Hey Can I Chan. Read it for more insights.