i think she should be okay. many of us lean way over our hadnlebars, putting much of our body weight directly onto the stem. compared to that, a couple gallons of milk are quite light. your wife should, however, remember that a lot of weight in the basket will interfere with steering. greater rotational moment of inertia means it's harder to steer the bike where you want it to go. it's not impossible, just requires a little more concentration, and remind her to give herself room for nice wide turns. to avoid this steering issue, try a rear rack. if your frame doesn't have the proper eyelets (your bike shop can determine this for you) they make racks that clamp only to your seat post. good luck and ride safe!