It is said that girls who like SpongeBob are very cute, very cheerful and lively. Your girlfriend is probably the same. If you have already decided to give her a doll, then give her a doll. However, it seems that the dolls of SpongeBob are usually only pillows.
If possible, you can give her two things, a pillow of SpongeBob and a cup with SpongeBob pattern. Pillows are something that girls like, and when it is cold, they will like pillows more (to keep warm =.=). Needless to say, you should also know the meaning of the cup. The meaning of the two together is "Baby loves you forever", because she likes SpongeBob, so the pillow can refer to her.
Girls who like SpongeBob should also like teddy bears. You can give her a teddy bear + a scarf. Don't buy the ordinary teddy bear. You can choose the one that glows (because it is fresh and creative =.=). The scarf is just when it is cold, and giving scarves between lovers represents warm love. The meaning of the two together is "I will accompany you for a lifetime and stay by your side forever."