"Neha and her friends are going."
Translation:नेहा और उसके दोस्त जा रहे हैं ।
Disclaimer: I'm not a native speaker, just another student like you.
Yes "uski" works if all the friends are women.
RagingFire4 is correct that दोस्त is a masculine noun, but it tends to be treated as having whatever gender you need it to. There are feminine usages of दोस्त all over the internet.
When I have a question like this, I'll Google for a quoted phrase like "मेरी दोस्त". Then I think about whether the hits' sources are credible. In the case of "मेरी दोस्त", I found a lot of hits involving professional communicators, e.g. on news sites and in book excerpts. So, what they say is good enough for me. :-)
And also, one of the phrases Duolingo uses in the Numbers skill is "नेहा मेरी चौथी दोस्त है।" Both "my" and "fourth" are feminine in that quote.
Firstly, oblique plural 'friends' would be दोस्तों; also your subject is just 'Neha' - 'Neha is going with her friends' - similar meaning, it's just a bit different, Duolingo can't possibly have every single variation and way of conveying a similar sentiment, so stick to fairly literal (at least grammatically equivalent - 'Neha and her friends') translations.