Need some advice on Gifting my GF.

I know I should decide on my own...but I never had a gf and gifted any girl... I don't even have a sister. So, me [24M] & she [21F] are in a relationship for 5 months. She likes signing and her vice is really really good. Also she likes cute stufss too. For her birthday i brought a dress that may look good on her. But I'm feeling like I'm not doing anything special. I just don't want to give her something too expensive, because it's still early in our relationship and as my earnings are almost 4x of her's that could really put a bad impression. I want to give her something useful that she can use too, I checked her online shopping app browsing and by the algorithm I saw she was looking into lots of Tumbler. But then I remember of her sister maintained it to me that she will give her that.

Help me out everyone. Im lost T_T