Based on chapters 2 (picnic) and 8 (beach), plus some info from chapter 12 and elsewhere, it's apparent Mina simply has no GPS or mobile internet connection to use while out on her own. She also can't call Super Mina because she has no cell tower access (all her calls are over the internet) and their wireless communication range between units is far too low. Most likely she simply looked up the directions from the home Wi-Fi and neglected to consider directions back home based on her presumptions and lack of experience outside (which she points out when going out for the picnic).
If you find it incredulous an advanced robot doesn't have these features, you have to remember Mina is among the most basic models of her series and Takuma could only afford her because she was used on top of that. Additionally, Mina's model is considered to be akin to an appliance and even Iida and Senju (the woman and Mina from the company that picked up and dropped off Mina before and after her upgrades) expressed their doubt of anyone seeing one as a family member. She may be advanced tech by virtue of being a robot, but she's still on the low end with plenty of features left out—even her eye cameras are barely better than a smartphone's, compared to Super Mina's 300x zoom with no visual resolution loss.
And yes she absolutely can lie, she even lied about when she'd be back from her upgrades to surprise Takuma.
If you find it incredulous an advanced robot doesn't have these features, you have to remember Mina is among the most basic models of her series and Takuma could only afford her because she was used on top of that. Additionally, Mina's model is considered to be akin to an appliance and even Iida and Senju (the woman and Mina from the company that picked up and dropped off Mina before and after her upgrades) expressed their doubt of anyone seeing one as a family member. She may be advanced tech by virtue of being a robot, but she's still on the low end with plenty of features left out—even her eye cameras are barely better than a smartphone's, compared to Super Mina's 300x zoom with no visual resolution loss.
And yes she absolutely can lie, she even lied about when she'd be back from her upgrades to surprise Takuma.
