I think 5 years is way too long too, it does sound like she is trying to deal with her own issues through you.

I have been thinking about the age gap with my kids, 22 months between dd1 and dd2 and 17 months for Ds and dd2. I would rather have them this age than a bigger gap it just seems to make more sense to me. The nappies, bottle feeds and toilet training will all be over sooner rather than later rather than having to adjust again.

The hardest thing for us is getting dd2 to be gentle with Ds, I can't leave the room with him on the floor. She is getting better though, and everything she does is out of love she is just a bit rough

Like everyone has said if it feels right for you then go for it!