The previous thread where I posted this seems to have vanished overnight but figured the information would be helpful to repost, so see below. Essentially, Michelle will be available without spending anything provided you are able to complete sufficient milestones and complete the roadmaps.
EDIT: Updated to account for confirmation of final events with items from GR here:
Dynamite / Level Ups
- The maximum possible dynamite is 10,250 and Michelle needs 3,000
- There should be 10 level ups during the event, meaning alternating hitting the 100,000 on five (5x225) and 500,000 milestone on the other five (5x375) is enough to hit your 3,000 dynamite if you are light on resources.
Sewing Kits / Raids
- There should be enough raids for 2,250 Sewing Kits (from milestones, not drops) and you need 1,000 for Michelle
- 3x1,800 trophies and 2x1,200 trophies will get you enough Sewing Kits.
Matchbooks / Wars
- There will be 2 wars, but if you haven’t got the 100 matchbooks already you probably shouldn’t be realistically considering your prospects of getting Michelle. It was something minimal like 5,000 to get the 150 matchbooks last weekend, and suspect the same next weekend.
- The wars should give you a total of 300 matchbooks.
Scalpel / Survival Road
- There should be 975 Scalpel’s minimum across five SR’s (including Faction SR on final weekend which finishes only a few hours before the collections end - so beware relying on this final event) and you need 500 for Michelle.
- Finishing Elite in four Survival Roads will be enough or three Golds and two Elites.
Obviously this is all based on some assumptions about event rotation not yet shown on the calendar, but given the repetitive nature of the calendar it should be pretty sound.
Masks / Roadmaps
- For everyone who keeps making spurious suggestions about them, 7 masks will be given out in the 7 roadmaps during the event. This is clearly stated in the in-game information. See screenshots below.