Elsie would’ve offered to take the lower floors specifically because of room 208, where Eva Ernst/the Grand High Witch was staying. Elsie would’ve peeked through her experiments and notes, and likely would’ve stolen the remaining bottles of Formula 86 for herself (Luke only took one of the bottles).
She’d have to spend a lot of time studying the GHW’s notes, because there are no witches left in England except for Miss Irvine, and she went turncoat and turned Luke and Bruno back into humans. There’s also no doubt that she’d spend time looking for Helga due to her having killed the GHW and thus being a threat to remaining witches, but there’s no way of knowing if she’s aware of Miss Irvine having gone rogue. If she does know, then she’s forced to devote her time between two major threats. If she doesn’t, then it’s likely that she won’t last very long.