Works for me! I agree with the group initiative, it really speeds up combat in PbP.
Umbriel's primary initial goal in Sigil is to learn a bit about what's currently going on in the city without getting into trouble, so tagging along with the more eye-catching members of the party makes sense for her. She's also quite intrigued by these chance-met companions, and especially wants to talk with Saffron about her plane-reading abilities. Getting in touch with any contacts can wait for later