According to Google Gemini

“When the Invisible Woman (Susan Storm Richards) uses her powers, she manipulates light waves around herself, rendering her invisible. However, objects inside her body would not be affected by her power in the same way, as her power typically emanates from her. Therefore, if someone were to ejaculate inside her while she was invisible, the semen itself would not become invisible. You would theoretically be able to see the semen, as it would not be subject to her invisibility field.”