I will not say what you can do. Illinois law only says what you cannot do. Not only can you not have sexual intercourse but there are a number of other acts that are considered illegally sexual, even if you don't think so. They are illegal, since she under the age of 17. Read carefully the definitions of "sexual conduct" and "sexual penetration" in the Illinois statute. Oral stimulation of your penis or her vaginal area is illegal.
First, note that touching/fondling by either one of you is illegal conduct.
Even if she is the alleged victim and is the one doing the touching/fondling of you your partner can be arrested.
Also, skin-on-skin contact is not required because touching/fondling over the clothing is also illegal. Many prosecutors have made the case at trial and no item of clothing was ever removed.
I think even if your seemingly innocuous behavior is permissible there is a fine line to be criminally charged if some attentive adult relative would perceive some impropriety and report that activity to the authorities. In that case, criminal charges are very possible.
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Respectfully, Attorney Alexander Ivakhnenko, Chicago, Illinois