I just checked the biographies again. Frank and Shannon were married for over 10 years, let's say 11-12 years. I'm not necessarily tech-savvy, but I doubt the messages would survive the time, I'm not sure if Lilith had a cell phone at that age, and in general it seems rather weird to me. Chances are more likely that the glove quote is more present day in nature. Especially the message with "Do you work tonight?".
Edit:
Speaking of biographies, I read Shannon's again.
"She began to resent Frank for being with Jessica (...)"
I have already written a few times that she is quite a... Pathetic person, from what we have seen of her. And it's not like Jessica and Frank became a thing after she moved away and broke up with him. While I can understand her not seeing any future in a long distance relationship, I still find the whole scenario with her a bit twisted. I kind of get the feeling that Shannon, either in her time when she was first dating Frank she suspected that there might be something going on between them or at some point in her later years this suspicion developed. Especially with a mini Jessica growing up under her roof and under her nose. Come to think of it, the woman has real complexes about Jessica and I'd love to know what Jessica's mentality would be about that: Would she be proud that her daughter is getting under Shannon's skin like this (for one thing because of the visual resemblance and then that she gets along so well with Lilith), would she be upset that Shannon can't put those old stories to rest and live her life, or would it be a bit of both?
And even though Shannon isn't the most sympathetic person I think a little subplot that life or some key events from her life show what makes her tick and why she does what she does.
Something like that is not meant to rehabilitate her as a person, of course, as far as that goes she's beyond the point of no return.
Points that would interest me:
Family life in Shannon's family (especially her interaction with her parents).
The reason for the conflict between Shannon and Jessica.
The breakup with Frank and her move
The reunion with Frank.
How it came to the fling with her ex-husband.
How she came up with the idea to charge Frank with the false allegations to the judge.