Lens as a gift, help!

Hello photography fanatics!

My partner likes to snap photos as a hobby. She mentioned wanting to get a new lens, and her birthday is coming up. So I will be a good partner and hopefully find a good one for her. The thing is, I don't have any experience with photography or lenses, so I'm hoping to get some help here. I've attached a few of her photos, that might help.

She currently has the following:

  • Nikon D5100
  • AF-S Nikkor 18-55mm 1:3.5-5.6G
  • AF-S Nikkor 55-300mm 1:4.5-5.6 G ED

What would be a good addition as a lens to either replace or give her new possibilities for taking amazing photos? Thanks!