A number of sources have been provided already. Another one that points to the fact that she was a harlot is in Sifrei Zuta - Bamidbar 10:29:
ד"א רחב הזונה שהיתה מזנה עם בני המדינה מבפנים ועם הליסטים מבחוץ שנאמר כי ביתה בקיר החומה ובחומה היא יושבת
Alternatively, Rachav the harlot offered her services to the people of the city within the city, and with robbers from outside. As it says, "For her dwelling was at the outer side of the city wall and she lived in the actual wall" (Yehoshua 2:15).
However, on balance, it is also worth noting that the Sifrei Bamidbar 78 understand this title of 'zonah' in a different way:
ר' אליעזר אומר: זו רחב הזונה, שהיתה עסוקה באכסנאי
Rabbi Eliezer says this is Rachav the 'Zonah' that was busy/engaged with an inn.
So in this context, the Sifrei chooses to understand 'zonah' from the word 'mazon', to provide food. Thus she was an innkeeper through which she earnt the means to feed her family. And as such she was referred as Rachav 'the feeder' and that is what 'zonah' means.
Building on what @user6591 said, I would imagine that a reason why we possibly don't dwell on the fact that she was a harlot was because she later converted and married Yehoshua (Megillah 14b) and was famed (like Yisro) for her righteousness (Yerushalmi Brachos 2:8)1, as such we don't draw attentions to a convert's past as it may be a source of great shame and embarrassment. As it says in Shemos 22:20
וְגֵ֥ר לֹא־תוֹנֶ֖ה וְלֹ֣א תִלְחָצֶ֑נּוּ כִּֽי־גֵרִ֥ים הֱיִיתֶ֖ם בְּאֶ֥רֶץ מִצְרָֽיִם׃
And a stranger [from another land] you shall not taunt and you shall not oppress him [by theft], for you were strangers in the land of Egypt [and are equally vulnerable to taunting].
1 It writes there: כך בשעה שישראל עושין רצונו של הקב"ה מחזר בכל העולם כולו ורואה אי זה צדיק באומות העולם ומביאו ומדבקו לישראל. כגון יתרו ורחב - At the time when Israel does the will of Hashem, He chooses a righteous person among the nations of the world and He brings him and joins him to Israel. For example, Yisro and Rachav.