Emoji's on S4

[silverpetals]

Ok mega confused right now. Whenever I send an emoji in a SMS it converts it to MMS as expected (which is why I never use them as no MMS are included in my plan) but my mom just got an S5 and she can send me emoji without it being a MMS message? She doesn't get the "converting to MMS..." message nor does it show as a MMS on my phone, just comes up as a normal text. How is this possible?