Some people are telling you to downsmash but unless you have a perfect read on which direction he is going to roll (in which case if you did you probably wouldn't have trouble with his rolling patterns in the first place) it's generally not a good idea. Rolling is purely a defensive option and it accomplishes nothing in racking up dmg on you towards a kill, but by going for a dsmash you are creating a free punish for him that just made all of his rolling rewarding because you committed too hard.
Your best option is run and grab. It's not as broken as earlier iterations but lucina/marth still have some pretty decent grab range and if you're fast enough you can easily get a run and grab for a roll punish. If you read it and you notice that he is rolling your direction as you are already running, do a pivot grab. It can rack up damage pretty quickly if you can get out your pummels and it will lead you into dthrow which will accomplish a lot for you against players that like to spam defensive options. By grabbing and dthrowing you not only accomplished beating the roll and racking up dmg for it, but now you have him in the air with a great juggler and more likely than not he will have habits in the air similar to what he has on the ground. d-throw to up-air works up until about 50% or so, ff u-air into u-air is a true combo if she's pretty close to the ground, which can happen quite often if sheik decides to air dodge (which she will, because if she's obvious enough that she just spams rolls all day, she is obvious enough to start spamming airdodge (or one, singular option that you can punish) after getting d-throw to u-air combo'd at earlier percents).
The most important thing is to be patient. Use shield to keep yourself safe, and while doing so instead of focusing on how you're gonna hit the sheik, pay attention and see where the sheik is rolling. Is she rolling towards you when she's cornered? does she roll away after throwing out (e.g.) a dash attack? Even top players have patterns (very few) so you will find that, against players that can only rely on spamming rolls to avoid you, there will be plenty of patterns to be found and it's something that you have to work at to get good at.