Good observation, she should look way bigger than Mary Madison. So either Mary is really close to 7k, or Lilly is really is close to Mary in size 
Mary lists herself as an M-cup, currently. She had listed herself as an L-cup until just recently. I don't think she's gotten all that much bigger in the last few months. Certainly not up to 7K. Did Lilly not get the fill recently she'd been talking about, perhaps? Anyone a member of her Patreon?
I dunno, maybe Mary has gotten bigger and just hasn't reported it.
Odd.