I would think it's enough, since you have the I-94 record/number. you should explain in the section for additional information the circumstances. Any copies/photocopies of the old passport / VISA? (i submitted both my parents' packets in December)
did your mom arrive in the US more than 10 years ago? if not you may also be able to get a record from CBP I-94 website. what visa did she arrive on?
This is a bit different, but i went through AOS process myself without the original physical I-94 record (lost it), but was able to use the original passport/visa with admission stamp