(heavy spoilers) my theory of Maggy's story + theories from the "Still Digging" single
So since Ridiculon finally decided to upload the full version of Dig Your Own Grave, full with a 1:45 minute intro, along with another version named "Can You Hear Me Gloria?" and that's got me thinking about the lyrics and how some things connect through the lyrics and the games.
TLDR; Maggy has heart cancer, and the events of Mewgenics, and whatever else Dr. Beanies did to her, caused mutations leading into the transformation into the mother, also Dr. Beanies is Isaac's great grandfather
I'll start with the fact that Ridiculon named the this other version "Can You Hear Me Gloria?", it's different from the others as it contains lyrics from specifically the female singer. So it's obvious the lyrics are targeted towards the player character which is where the connection of Gloria=Maggy comes from, and would explain the connections between how the radio host might be Isaac's dad since he mentions the name Gloria multiple times.
Secondly, the intro of the single "Still Digging" has the radio host talking about grave digging, and its cousin grave robbing, but most importantly mentions how his "granddaddy was a very very famous, uh, doctor" and his duties to dig up bodies, and recently executed criminals (origin of butch??). But the importance of this is that if this is Isaac's dad, then Isaac's great grandfather was Dr. Beanies, and would explain how things like the bloat and other flesh creatures exist in both Isaac's head, and in real life (Mewgenics)
Anyway, my main theory is about Maggy, how she is the mother in the end area (and maybe Edmund retconned that she is also the mother in TEIN). The reasons for this mainly come from TBOI, the fact Isaac is happy to see cancer, + he specifically finds a heart. If Maggie knows has heart cancer that makes sense why Isaac goes "yay, cancer!", as he knows he will eventually be free, and the cancer will take her life (subconsciously maybe, I dont think isaac is that smart).
Now that we assume Maggy has cancer, this explains the excessive use of tumors in TEIN and the end area in Mewgenics. since Dr. Beanies revived us, and we've seen his experiments in the bunker, we don't know what he's done to us. Knowing that the time machine also causes random mutations to cats, and it definitely affects Maggy, as she travels with the cats numerous times over and over and over, now it would make sense that her body will eventually deteriorate and become consumed by this mutated cancer, and it begins to spread throughout more than just her own body, and she becomes one with the earth.
My final take is regarding her heart metaphorically, now that she's fused with the earth, her love for her family has been corrupted by this mutated cancer, and fused to the earth as well, shifting her "mind" to care not about her own blood and family, but with the earth as well. And since the same energy that mutated her, also mutated the cats that visit her every time you take a run to the end, maybe she can sense it and that's why she thinks they need to "return" to her, from her battle intro quotes.
(I have another theory regarding how Nona and Jack are actually a failed clone attempt of Maggy and Isaac, which brings the idea of her corrupted metaphorical heart, and that's why it failed, ending up with the Maggie clone dead, and the Isaac clone alive, as a twist to what happened in TBOI)