jewishfeminist02 –
My first thought was that the tattoo might qualify as a chatzitza at the mikveh. On further reflection, I realized that anything– including a tattoo– that is a permanent part of a woman’s body is not a chatzitzah.
There are many reasons why it would not qualify as a chatzitza.
1) It is under the skin, so it is not somewhere that water could reach anyway.
2) It is not significantly tangible (much like hair dye and nail polish which are generally not chotzetz according to the letter of the law)
3) It is something which people normally do not remove. A chatzitza on less than the majority of the body which one generaly does not intend to remove is not chotzetz according to the letter of the law.