Does anyone know how often an Act 91 notice needs to be sent to a borrower who is consistently more than 90 days late on their Home Equity loan?

"Act 91" sounds like a reference to a state statute. Since you're in Pennsylvania, I did a little digging at the Google mine. There were a number of references to Act 91, including a sex offender statute and a separate one dealing with minors. But I think that the notice you're asking about is required by the Commonwealth's HEMAP program.

Here's a link that may prove helpful: http://www.scolierilaw.com/homeowners-em...ces-reinstated/

I read thru the page at the link, and there doesn't appear to be anything that addresses your question. You may find it helpful to repost your question in the Pennsylvania forum, where another lender who has already dealt with the issue is more likely to see it.