Yes, of course she can learn! That's why they call them "social skills".
And whilst you cannot instruct her, exactly, you can guide her in the right direction. It is very hard though, if you are in lockdown, as she needs to practice.
Aged 7 many girls are in groups not with one BFF. You should manage her expectations - first step is to find some nice girls or boys (but typically at this age, it's girls) to join in with during break time. Can she identify someone who seems nice, and then be very brave and ask if she can play with them? If the answer is no, then not to worry she can try another day. But most kids will say yes in that situation.
Does she know The Roolz of playing nicely? Eg taking turns, being kind, not being bossy, not overreacting when there is a disagreement and being able to resolve arguments. These are things that can be discussed and taught.
If she is prone to tears at the slightest thing, can you help her manage that by helping her to think through how it impacts the people around her? She is old enough to put herself in someone else's shoes,and crying might seem like a short cut to getting what she wants but actually it is important to use words instead as often as you can, as we can't all go around crying every time something goes a bit wrong, just imagine! Point out to her in situations when you find things are going wrong for you and explain how you manage frustration and sadness without crying by trying to solve the situation through action or conversation, or walking away until you feel calm, or whatever.
You can find a book or TV program to help - Worst Witch or My Little Pony might be good - something that deals with friendships and moving to a new neighbourhood or school. Ask her how the character was able to make friends. Talk to her about how a character might have felt in a situation- eg nervous when the other characters are already friends, and how to put on a big brave smile and ask nicely if you can join in.
If possible speak to Class teacher and ask her to keep an eye on her. Teacher may be able to steer her towards a buddy or a welcoming group of girls.
You can also do your bit behind the scenes, see if you can have a park play date after school or at a weekend.
(This is all assuming no lockdown applies, I have no clue what you can do in lockdown except beg to join an online Brownie pack, or some similar online club).