Maybe she should leave the tattoo. It could remind her that she needs to find out much more about boyfriends/friends before she makes any decisions that will have life-long consequences (having sex, unsafe sex, drugs, tattoos, etc.) and it might remind her that even if she makes a wrong decision, she is capable to doing better and accepting the consequences with her head held high. It seems that she feels that she did the tattoo to remind her of her boyfriend rather than because she thought it would be nice to do it for herself.

Regarding only children and IQ's, the study only found a correlation, not a causality. It could be that there is a strong genetic component to IQ scores, and that people with high IQ's are pushed toward a career-focused lifestyle. People with a strong career-focus tend to put off child-bearing and have fewer children.
So maybe they don't have high IQ's because they're only children; perhaps they have high IQ's because their parents have high IQ's, and they are only children for the same reason.