Is it normal to be attracted to your girlfriend's mom?
Mostly.Normal for most people
Yes, you can find your girlfriend’s mom attractive without it meaning you want to betray your girlfriend. The important part is keeping respectful boundaries and not acting on it.
Attraction can show up in inconvenient places, including with someone who’s off-limits. A passing crush or noticing someone is attractive doesn’t automatically say anything deep about your relationship or your character.
What matters is what you do with it. Don’t flirt, make a move, or put your girlfriend or her mom in an awkward position; keeping it to yourself and letting the feeling pass is usually the kindest option.