Is it ok to name a Muslim baby Gabriel or Gabriella?
I think it's okay. I believe the angel Gabriel is common to all three monotheistic religions. The only difference is that in Arabic.....Gabriel is pronounced Jibreel. But it's the SAME thing.
You can all a chair a "chair" or a "chaise" or a "kursi". It's still a chair.....the object doesn't change. Gabriel will more than likely be pronounced as Jibreel by desis/Muslims and it should be fine.
I'm not sure about Gabriella though because I've only heard masculine names for the angels.....never feminine names. For some names....there is a female variant. For example.....Jameel and Jameela or Shahid and Shahida. Haven't heard of Jibreela. Or for the angel Mikail......I've never heard of Mikaila.
You could ask this question in the religion forum.