Hi Erin Camp. Welcome to Grokker! And congrats on getting back into working out!

I would take the approach of trying to build muscle, as that would likely result in healthy weight gain. Some tips on buliding muscle:

1. You will want to lift heavier weights to stimulate muscle growth.
2. Aim for lower reps (6-10) so that you can lift the heavier weights while stil keeping the proper form.
3. Work each muscle group twice a week as that is the most effective way for building mass.
4. Make sure you are eating enough protein to build these muscles.

Here are a few programs you may want to check out:

Kelly Lee: Strength Training - https://grokker.com/fitness/strength-training/program/back-to-basics-strength-training-with-kelly-lee/57e41a940534ba273d9aee5e
Total Strength with John Godfrey - https://grokker.com/fitness/toning-and-sculpting/program/total-strength-with-john-godfrey/56b4e88a078a36e2053130dc
Pace and Go: Train and Transform - https://grokker.com/fitness/interval-training-hiit/program/x5-intensity-workouts/5501ca073988e3942624e385