I think talking about class is useless, according to http://www.cbradio.nl/intek/intek_512.htm it can only be stretched after 28,310 / 28,305, where neither AM nor FM can accommodate the modulation width.
Her sister's hair would be stretched to a reasonable segment http://www.cbradio.nl/intek/intek_520.htm , but the station modified in this way may not then be used for CB. Also, the frequencies will be approx “okanalovane” with various skips, I assume that, as with other CBs, it will not always work after 10kHz, but some frequencies are skipped, some flipped, it happens to be shifted in frequency “base 40K” channelovanie . http://www.scbr.sk/legislativa/vypis-frekvencii-cb-pasmo/
Also FM / AM is used on 10m with another type of modulation at least, although sometimes something is found, mainly operators and amici.