I continue to believe that it is unlikely that your daughter is a major. Normally, major would have manifested by now. Instead, her Hb is rising, which may be the effect of wheatgrass. The full effect of wheatgrass takes some time and it is thought that a full year of using wheatgrass is necessary to see the full effect. Please continue her on wheatgrass and folic acid if you have not yet started that. Both gene mutations you have previously mentioned are often found in thal intermedias although there is no certain way to know if the genes will manifest as intermedia or major. Also, if there is the presence of the alpha thal gene it can act as a moderator of thal and present as intermedia. Do you know if either parent carries the alpha gene? DNA testing may be the only way to get definite answers at this point.
A 19 month old child with an Hb over 10 is very unlikely to be a major, but it may be some time before you can be definitely certain of this. Since wheatgrass does seem to be having a positive effect I will have to disagree with what the doctors told you about hydroxyurea. The raised Hb does show an ability to create fetal hemoglobin, which is the main deciding factor for giving hydroxyurea. If later on she does have a drop in Hb below 8 I would seriously consider hydroxyurea before transfusions. For the time being, continue with what you are doing.