The true recommended daily allowance for vitamins and minerals is probably based on sex and your body mass. They just list the percent RDA for an average sized person. If you don’t need a full 2000 calories worth of energy, you’ll still likely get all the vitamins and minerals your particular body needs since your requirement for these will be prorated down. I bet it’s proportionate enough that you may not need to worry. Just eat as much Huel as you feel is right for you, and you’ll probably automatically get all the micronutrients that you need. Also, I think the RDA values are rounded up and are likely overestimated anyway. Also, the human body can recycle nutrients if needed.
Correct me if I am wrong, but the DV of vitamins is based off a 2,000 calories diet. If you’re eating less than 2000 calories, than you needn’t worry about the vitamins. Even at 1300 calories of Huel, I wager you are getting more vitamins than 85% of Americans.
And if she is truly worried, she could take a half Centrum multivitamin a day on top of her 1300 calories of Huel to supplement any she feels she needs more of. Although this would likely be overkill.