The short answer generally would be that it would be up to the committee to make a decision like that. Members of the committee know that on consideration of a draft report, any decisions related to its contents would be for the permanent members to make or any member properly substituted for a permanent member.
In terms of decision-making, unless Madam May were substituted for one of the permanent members, that would not be something that would generally be envisioned. However, the committee could always make a decision to share the draft report with another member or with Madam May.
As well, there would not be anything stopping Madam May from making suggestions to the committee if she wanted to. She could send suggestions to the committee for them to consider and then accept or reject.