Can a Letter of Recommendation be effective without much coursework

I’m applying to grad schools this coming fall and have 2/3 letter writers lined up, and am just trying to make a decision about the third. I took two classes with this third letter writer about two years ago, one survey course and one directed reading. We spent a lot of time in her office hours chatting and she got to know me as a student, and I achieved A+ in both courses.

However, both of those courses were two years ago, and we haven’t had much interaction in the interim as I’ve been completing credits for my other major. I was planning to take a seminar with her this fall so as to get a third course in with her, and also one which is more recent so that I’ll be fresh in her memory. But, the course conflicts with pretty much everything else I was hoping to take this academic year, including some courses much more directly related to my research interests.

Was hoping to solicit some thoughts on whether a LOR can be effective a) without much coursework and b) with not-so-recent coursework, providing that the coursework which was done was completed with great marks and lots of professor-student interaction. In other words, even with glowing comments, will a committee always look negatively on letters based on out of date courses (completed in 2nd year, for instance) and not that many of them, to boot?

Thanks