As Ms. May said when she exited, the rules were recently changed in the House to allow non-party-status members to bring amendments to committee. What happens now with the rule is that if it is possible to bring the amendment to committee, you cannot then bring it at the report stage in the House. Therefore, Ms. May cannot participate in this, and therefore, her privileges are being impacted because she is no longer able to speak to her amendments.
On May 22nd, 2018. See this statement in context.