See my #108 with precedent, the protection doesn't apply at all to criminal offenses. The officer could have immediately cuffed her and hauled her off for assault. Of course he didn't want to risk his career in doing that, so he was smart and let the higher-ups deal with it.
Excellent.
Some might try to make the case that she "breached the peace", but it appears to me that the burden is on the Capitol security to know who are members of Congress and who are not. They have no power to detain a member of Congress. Congress itself lacks the power to authorize the Capitol police to detain one of their members.
She could be expelled from the House, though, if Congress decided they would be better off without her. This requires a two-thirds vote of the House to expel her.
Others have commented on a recent incident when a committee chairman ordered the physical expulsion of members of Congress from a meeting. This appears to me to be a violation of this Constitutional protection. The chairman should have brought his complaints to the House itself and asked that they be punished or expelled.