Experimenting with Ignem just below the library is like bringing an open flame into the library-- it is simply Not Done. She can lie about it, but if she's caught, that's sufficient to get thrown out of the covenant. Dunking Maribus' journal in a lake was enough that no one trusts her as far as they can throw her; if she destroys the rest of the library, she will be killed in her sleep.
If Sinmore wants to use someone else's lab for a season, she will have to work something out with that character. I am not sure about the lab rules from covenants, but there may be a penalty for using someone else's lab if it isn't totally generic, but some of the specialized labs may have enough bonuses to offset it. I'll have to look that up when I get home.