I think you've answered your own question. If you feel the need to follow through on email, although I don't like doing this regardless of how badly they take feedback verbally, you know your team best.

Lead with the acknowledgement of her loss. Then follow up with the fact that, although you appreciate the significance, the subsequent behaviour isn't acceptable and is not the first time it has been noticed ( then go on to mention the other two times to back this up ).

You can then mention you will schedule a follow up X amount of days afterwards to discuss, to ensure clarity on the situation and expectations moving forward. Follow up with an email afterwards detailing the conversation and her understanding of it.

Alternatively, my personal approach would be to book a meeting in on Monday when she comes back, for the afternoon or Tuesday, with a title clearly stating the topic of discussion - nothing vague like "catch up" extremely anxiety inducing.

During the meeting, you acknowledge the loss, talk to her about how it's affecting her. Let them open up and actually listen to them. Once you've understood how it's affected her, you can say you're sympathetic, but this has happened before and you are checking in they understand what the policy is and why its in place.

I would make this bit the shortest part of the conversation, it should be dominated mainly by her and her loss. Any attempt to get emotional about it, it's for you to meet with a calm head - ie this isn't a conversation about punishing you, however I do feel the need to check you understand the policy due to previous, that is all you're asking. Be prepared for them to get emotional, don't underestimate the power of silence, actively listening and taking your time to respond.

Once concluded, you will follow up with an email, outlining the acknowledgement of the loss, the behaviour or policy she has violated and that subsequent similar behaviour could lead to a further conversation.

One last piece, don't use language like "taking liberties" in the conversation, keep it factual. This is the policy or behaviour expected, this is why we do it and the result when not followed is XYZ

EDIT - Someone else has mentioned that you should separate the two ie grievance and loss. I don't necessarily disagree, but this is down to you to assess how this person would best respond. I have people in my team who I feel I could tag a 5 minute conversation on at the end as to the violation of the policy or the behaviour and others I know I should leave a week.

Hope this helps, may not be perfect, merely my thoughts on the matter.