There are free scripts around, but first you/she will need to know what is offered on the website. I've been making websites for clients since the mid-90s but have never used Frontpage, so sadly cannot offer advice on that.
There are free scripts around using PHP or CGI but there are some scripts which are disliked by hosting firms because of security issues.
On the other hand, some hosting services have their own scripts available for customers to use, or offer software on the control panel, which will install things for you. (For example, on some services I've seen "Installatron" while on cPanel there is often an add-on called "Fantastico". Fantastico is the one I've used most, and offers options to install software to provide photo galleries, feedback forms, web forums, etc. I just found a list of software for Installatron but then looked for Frontpage Contact form and found this one...
Form using FP 2002 at Linda's "www.personal-computer-tutor.com"
Obviously the more complicated the form, the more work you might need, and I've used/ seen various forms which do some validation of fields with Javascript to check user has filled in particular items before allowing them to "submit".
I'd say the first thing to check is whether the web hosting service has particular guidelines or offers their own scripts, then look for something that does validation of fields if your client has indicated she "requires" certain fields are filled in.
Hope that helps you on your way!