It’s just such a perfectly ‘Yennefer’ thing, to ensure she can be contacted, but ONLY on her terms, only when the situation is perfectly within her control. And it’s such a NOT Yennefer thing to relinquish that control to anyone, which is what makes it profound if and when she does it for Geralt.
Honestly!! This is what kills me about her inviting him to her home, because that was more than just committing to the relationship, it came with the knowledge that now everyone would know. They would know she brought this man home, and he is a witcher. Their affair would be public within her circle and within the court. So it was a major step for her, as some one who loves her privacy as much as she does and also as some one who cared greatly ( at that time ) about her standing and position.
The same with the party at Thanedd. Her bringing him there when she tended not to bring dates at all was such a bold statement, something that she had never done before, and showed the level of commitment to the relationship she felt. And showed Geralt’s commitment too, as he seemed to sense the sort of association this came with as well as the judgement, and projected his own dedication.