Does she like going to the theater, or does she like watching movies with you on the couch?
If the theater, movie tickets make an awesome gift, and you can usually get a gift card with a pair of two tickets pretty cheap!
If at home, make a movie gift basket! Go to the dollar store, and find her favorite candy, soda, etc. Grab some microwave popcorn. Pop it in a cute basket or even one of those plastic popcorn containers (or go to your local theater and see if they'll give you one of their cardboard ones for free...) You can throw a DVD in there, too, or one of those Redbox rental coupons, if you have that in your area.
Disclaimer: these are just a kickoff to get you started. Obviously, you know your girlfriend, your budget, and what's available near you best!
First things first...
How about a Funko doll relevant to her interests? https://funko.com/
How about a sock monkey hat for her Funko doll? https://www.etsy.com/listing/224767016/for-funko-dolls-miniature-sock-monkey
Baking
If she likes baking and Doctor Who, what about this cool TARDIS cookie jar? https://www.amazon.com/Doctor-Who-Tardis-Cookie-Lights/dp/B000VQZOLS/
Speaking of baking, this set is really cute and colorful: https://www.amazon.com/Joiedomi-8-Pieces-Silicone-Including-Chocolate/dp/B01H45ZGVQ/
Cake Decorating
How's she doing on tools?
Does she need tips? https://www.amazon.com/dp/B01IBFP7GW?psc=1
What about some inspiration? https://www.amazon.com/Ideas-Decorating-Cupcakes-Cookies-Cakes/dp/1592536514/ (They even have new copies of the book available from third party sellers for cheap!)
Watching Movies
Does she like going to the theater, or does she like watching movies with you on the couch?
If the theater, movie tickets make an awesome gift, and you can usually get a gift card with a pair of two tickets pretty cheap!
If at home, make a movie gift basket! Go to the dollar store, and find her favorite candy, soda, etc. Grab some microwave popcorn. Pop it in a cute basket or even one of those plastic popcorn containers (or go to your local theater and see if they'll give you one of their cardboard ones for free...) You can throw a DVD in there, too, or one of those Redbox rental coupons, if you have that in your area.