If she's drinking a litre and a half a day she's probably used to quite a flowrate, yes. So if she behaves the same tomorrow, yes, try making the hole a little larger.
Temperature will be key, some lambs only like milk at the temperature they like..
Most like it blood heat (which feels very warm but not ouch! Hot! on the back of your hand) and very few like it tepid.
Are you feeding the same make and formula of milk as she's used to? It will be much easier for her the fewer differences she has to get used to.
And are you sure she needs a heat lamp? If she's got good shelter and plenty of clean dry straw, she probably will be warm enough in her sheepskin coat
She may well miss having other ovine company - I'd expect her to bawl the place down if that's what she's missing. I assume you plan to get her some company when the opportunity arises?