Maybe invite them round for a playdate?
A play date sounds a good idea! It can be so difficult at that age, bless her my heart breaks for her. Try get her in some clubs outside of school as that’s a great way for her to have friends outside of school, it kind of takes the pressure off her during school. Is there any other girls or boys in her class you can encourage her to talk to/play with xx
My child is quite a bit younger - but hypothetically, maybe - I would perhaps seek out children outside of school for her to be friends with , eg take her to a group (brownies, karate- swimming ?)- and maybe make friends (if you aren’t already) with some other of the other parents at the school - so you can do playdates - and help solidify friendships with girls (and perhaps boys?) who aren’t this ‘mutual friend’- also could you also arrange for her friend who moved away and her to talk on the phone or for them to write to each other going forward - sounds really tough for her 💕