You may NOT need 'macro' lens at all. 'Macro' technically refers to lenses which are designed specificially to do three things...
- photograph an object on film/sensor at [<30% of real size] to [>500% of real size] (figures provided for conceptual understanding only; photographers will hotly debate the numbers!)
- photograph a flat object (e.g. postage stamp) and have the entire flat object fall within a flat field of focus (not a curved field of focus)
- photograph at very close distance with minimal color abberations (which are caused by the fact that red light focuses at a different place than blue light -- and most lenses do not correct for this at super close focus distance)
If your SO uses her T4i camera with a true macro lens, here is what she can fit on her camera sensor, small objects...
- at 1:1 (lifesize on sensor), a photographic area of 15mm x 22.5mm
- at 1:2 (50% of lifesize), a photographic area of of 30mm x 45mm
- at 1:3 (33% of lifesize), a photographic area of 45mm x 67.5mm
- at 1:5 (20% of lifesize), a photographic area of 75mm x 112.5mm
IOW, unless the flower is smaller than 2" (about 51mm) across, a macro lens will not capture the entire flower in the frame of her camera...and if that is not what she wants to do, she does NOT really 'need' a macro lens, as you and she might think she does.
An investment in a relatively inexpensive and short 'automatic extension tube' might be more than enough for all of her photography of flowers, using the lens she already has! In fact you can buy a set of 3 different length tubes from Best Buy on sale now for $25, or spend $110 for a Kenko set of extension tubes
https://www.bhphotovideo.com …o_Extension_Tube_Set.html
or get any one of these from Amazon
https://www.amazon.com …ywords=EF+extension+tubes