Both of those are strong overreactions. Lassie shouldn't attack you if you simply try to take her armour, you should have to attack her to get it. Making it restricted but exchangeable for other armour. Accepting Lassie into the party prevents you from getting an unrestricted version from her, so no taking it off and stabbing her in the back, you murder hobo
Other Gith I can agree should notice and be badly disposed against you for wearing Gith armour, but not just having it in your inventory, and it should be the same for any Gith armour, not just Lassie's.