Tips for bedtime

Hey girls, I’m 17 and just graduated and currently pretty much have full care of my 4 month old niece and essentially have since birth (on the occasion her parents wanna see her/look after her) but right from the start she was a great sleeper (first few weeks waking up for feeds every 4 hours or so) but for the last month and half sleeping the full night (around 7pm - 10:30pm feeding then right back to bed around 11pm-7am) however the last few nights have been rough she’s been waking up around 2 am giggling and happy (ready to play) then till 4/5am it’s a struggle getting her to sleep..

I’ve tried dummies, putting comfort items with her/rolled up blankets beside her to give the feel of me with her, giving her a snuggle, giving her a bottle (Obv not forcing it but giving if she wants it) and also changing her nappy.. she is starting to get teeth and I though/think maybe this is the cause however she isn’t waking up upset/grumpy

Anyone else have this? Or any tips to help them sleep