Lenna Marsak -- who threw up the IG post that J Lo liked Thursday, touching on unhealthy relationships -- tells TMZ ... she definitely doesn't know J Lo personally, noting that they don't even follow each other, but has a sense of how her upload made its way to Jen's feed.

Lenna says the post in question had already been doing well -- in terms of performance and shares -- so it's possible Jenn just stumbled across it on her explore page on IG and liked it.

Remember ... J Lo liking the post caused a frenzy as rumors swirled about the state of her marriage with Ben Affleck. Since then, Ben has been seen coming and going from a rental home in Brentwood, as opposed to the $60 million mansion he previously shared with his wife.

We did see Ben and Jen reunite for the first in public Thursday night -- with both of them coming together for an event at Ben's kid's school ... but there was no PDA at all.

In fact ... we saw Ben drop Jen and her daughter at the Bev Hills home -- with him driving back to his rental, clearly indicating he wasn't spending the night at their marital crib.

Anyway ... despite the assumed troubles in Ben and Jen's marriage at this point -- Lenna tells us she has no plans to reach out to J Lo ... but is wishing the A-list couple all the best.

Lenna's decision is nothing personal to Bennifer, BTW ... she simply doesn't have time to help her out with her relationship woes -- as she's incredibly busy these days with her master's program. Ditto for everyone else in her DMs ... and she says there's a lot.

Unfortunately for them ... Lenna says she's not taking any new clients at the moment.