12 week old fighting me at nap time?

I am a SAHM of a 12 week old baby girl. She has never had a problem taking naps. (Except the fact that I have to hold her the entire time to take them) And don't say anything about me "spoiling" her because it is either that or have a very fussy baby. The last 2 days she has been fighting going to sleep to the point of screaming when I am trying to rock her to sleep. I know she is tired because I know all of her cries and can tell when she is tired. I feel so bad because I feel like I am abusing her or something! I know that might sound crazy but it makes me feel really bad. Should I just let her scream while I rock her? What else could I possibly do? Nursing doesn't help she just turns her head away and keeps screaming. Is this normal for that age?